Coil Testing
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Thread: Coil Testing

  1. #1
    Registered User Array dann's Avatar
    Join Date
    Jan 2005
    White Rock
    '04 GSXR 600

    Coil Testing

    I suspect that I may have a coil problem. I went to check them earlier today with my crappy tire digital Ohm meter and my trusty manual.

    My 97 GSXR 750 uses 2 coils, one for plugs 1+4, and the other for 2+3.

    I checked what my manual called the primary coil resistance which is between the pos. and neg. terminals on each coil. It said it should be between 2.3 and 3.3 ohms. It tested 3 ohms... good.

    I went to check the secondary resistance which my manual stated is between a plug cap and the coil. The manual also stated in another part of the book that the secondary resistance is found between 2 plug caps from the same coil. Although this confused me a bit as I didnt know which one was correct, I found was only able to get a reading between the 2 caps and not the cap/coil. The manual stated it should be between 3,000 and 4,000 ohms. My reading was about 36,200 ohms...I think.

    My ohm meter (mastercraft) reads ohms under either 200, 2000, 20k, 200k, and 2000k.

    While at the 20k setting I would not get a reading. When I tried at the 200k setting it would read 36.2. Im guessing I did this right?

    My bike still runs with the resistance 10x that of whats stated in my manual which also says coils would need to be replaced right away if theyre off.

    Does anyone spot any errors im making or have any suggestions as to other ways to check my coils?
    "It is better to die on your feet than to live on your knees."
    -Emiliano Zapata

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  3. #2
    Registered User Array
    Join Date
    Mar 2003
    Although I not an expert on testing coils I havent had to do mine.,..
    Fire up a Dyna 2000 ignition and get rid of those stock coils and ignition..... there going on ebay all the time..
    and it WILL be worth the few extra hundred it costs... Ive seen dyna 2000's go for 130USD ......

    Just my Opinion.....


  4. #3
    Moderator Array TeeTee's Avatar
    Join Date
    Feb 2002
    Out to pasture in the 'Wack
    04 Kawi Z1000,
    There's always room for errors when describing procedures.

    Simple, you've got two coils. Test and compare values taken under a number of conditions between the two. If they are the same and the bike runs then both coils are good. If they are different then one is bad. If the bike runs on two cylinders you will know which one it is.

    Coils are pretty much a works/broken deal. There is seldom a middle ground and when there is it's because it's intermittent which is still works/broken but rapidly changing.
    A backyard mechanic without a service manual is just like a hooker without a lamp pole.... they are both in the dark.

  5. #4
    Registered User Array Biper's Avatar
    Join Date
    Mar 2005
    2004 F4i
    A must when testing coils is checking the peak voltage while the engine is cranking. This method and the correct value should be listed in your manual.

    Otherwise it's the potential between the pins. Typically sitting at 12V when it fires there is a moment when the high voltage from secondary winding reflects back onto the primary winding. This value will give you an indication of the voltage of your spark which is the critical value. Acceptable range has alot to do with the specific type of coil but it should lie around 150 to 600 volts.

    You can use your hand held multimeter but will need a little gizmo in between it and the leads that will "hold" the high voltage reading so that you can read it. It should be available at most automotive shops.

    Could you tell us why you think your coils are shot? Have you checked your spark plug gap?

  6. #5
    if it ain't broke don't fix it. if a coil craps out you will know it. until that happens i wouldn't be worrying about it. stock coils usually last over 50k kms.

  7. #6
    Registered User Array
    Join Date
    Sep 2004
    You need to test the secondary circuit output first. This is the high voltage produced by the coil to fire spark plugs.

    Unless you have access to a specialized meter that is capable of reading this kind of voltage (20,000 volts +), you can measure how far the spark can ark to give you an idea.

    I have a mercatronic spark checker which works quite nice. Or you can place a screw into the high tension lead(spark plug lead), and hold it up to half an inch from engine ground. It should arc a good 3/8 inch if everything is good. If it is under 1/4 inch you have a problem. This is an easy way to isolate or determine a problem. You should have all the plugs pulled out when you do this making sure the plugs and/or leads are grounded before you crank. If not, you can damage the ignition system.
    DO NOT hold the leads with your bare hands. Use something to insulate. A cheap plastic tool is available almost everywhere to do this. There is more than enough voltage to alter your heart rymthm leading to heart attack.

    If you have good spark on all leads, then you can assume the ignition is fine.

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